Re: discrepancy with variable assignments and simple commands between sh

From:

Jan Schampera

Subject:

Re: discrepancy with variable assignments and simple commands between sh and bash

Date:

Wed, 25 Aug 2010 07:39:26 +0200

User-agent:

Mozilla-Thunderbird 2.0.0.24 (X11/20100329)

Mike Frysinger wrote:

On Wednesday, August 25, 2010 00:59:58 Jan Schampera wrote:

Mike Frysinger wrote:

the difference here being the value in variable "a" after function "f"
finishes executing. i was expecting the behavior of `bash`, not of `sh`.
i cant seem to find anything covering this in the man page except for
perhaps interpreting the meaning of some sections to mean this behavior
is allowed. but i certainly didnt locate anything that would imply
behavior of this would differ across bash and sh ...

I'd expect "VAR=VAL <simple command>" to behave like in your "bash"
example, in any case (i.e. also for functions!). Just intuitively, I
mean. I don't know any standard documents about it, maybe it is
"implementation defined", as so often.
Dash behaves the same way as your "sh" example, Korn too. Z behaves like
the "bash" example here. So I fear it actually isn't standardized and
you can't operate with functions the same way you operate with separate
processes.

unfortunately, ive relied on this bash behavior in the past in bash-specific
scripts because it's an easy way of tweaking a variable's value for a specific
command without having to save/restore context. which is why i was surprised
when it didnt work in a #!/bin/sh script (which had sh->bash). not that
standards bodies care about the pains they inflict upon me ;).

-mike

Okay, I think I found something
[POSIX excerpts]

- When a function is executed, it shall have the syntax-error and
variable-assignment properties described for special built-in utilities
in the enumerated list at the beginning of Special Built-In Utilities .
- Variable assignments specified with special built-in utilities remain
in effect after the built-in completes; this shall not be the case with
a regular built-in or other utility.

[Bash docs about POSIX mode]
24. Assignment statements preceding shell function calls persist in the
shell environment after the function returns, as if a POSIX
special builtin command had been executed.
Conclusion (still waiting for the Austin Group undercover guy):
- POSIX specifies this behaviour